Hi Michael,
My car is a 63’ E-Type coupe, built in Nov’ of 62’.
The thermostats came from the usual suppliers.
I’d have to search my records for part numbers.
I would like to find one with a larger diameter sleeve, it should help.
Alan.
It’s likely the SNG C3171/1 that we’ve been speaking about. As I’ve mentioned, it’s cut down from a land rover thermostat, and so has a somewhat smaller sleeve. You only have two choices if you’re looking for a tighter fit. The first is to use an original style bellows thermostat, or the modern Moss interpretation. The other is to use a Land Rover Series IIa thermostat, which is the source for the SNG version. In it’s unmodified form, the sleeve is a bit over 48mm. The problem with using the Land Rover stat is that you would need to machine the thermostat housing cover to accomodate it, as the shoulders are a bit too high.
That’s something I’ve been wondering about. What if you plugged the bypass and removed the thermostat and ran with all the coolant circulating through the radiator all the time?
Warm-up too slow I suppose, more wear in the bores according to your GM charts? No good for anybody who drives their cars in winter and actually needs a heater.
From what I have read about no thermostat: …for street (not race where they do …do that as they run at hi rev, WOT a lot)…has downside: if the cooling system is efficient the radiator will cool too much:,a thermostat should cycle open/closed to maintain op temp in the 70-86C range…some early stats were 63 or so.). that is the battle thermostats do with heat/cool. the radiator cools, and the thermostat says …wow…too cold…and closes flow to the radiator…then the thermostat says…oh,…too hot…and opens,. If the op temp runs too low all the time…the engine is not at its most efficient design temp, as determined by the engineers that set the thermostat temp spec in the first place. Tolerance of moving parts interface is thus different, lubricity of oil due to temp (tho true that oils are much better now than then, with heat and pressure), and intake fuel mix temp, combustion and who knows what else. It has been said/disputed that Flow may be too high and create cavitation at the pump. What say you Michael? Perhaps by accident Jaguar solved the issue of an engine running too cold…by having that almost never be the case with the XK120…it takes a cold cold day for that to occur.
Here’s a third option. Because the thermostat housings are cast aluminum, many are in poor condition due to 50-60 years of use and corrosion. Below is a photo of the thermostat housing in a well used XK140 intake manifold.
In addition to an original factory-cut bypass slot which is a poor fit to the correct Smiths thermostat, there is an abundance of pitting on the interior walls of the thermostat housing.
A solution would be to find a machine shop that could insert a brass or stainless sleeve into the thermostat housing. The inside diameter of the sleeve should be closer to the outside diameter of the sleeve on the thermostat. Then the machine shop would cut a new bypass slot in the new sleeve that better matches the travel of the sleeve on the thermostat. On the XK140 manifold, I would envision the new bypass slot being narrower and more towards the mid-point of the original factory-cut bypass slot.
" What if you plugged the bypass and removed the thermostat and ran with all the coolant circulating through the radiator all the time? Warm-up too slow I suppose, more wear in the bores according to your GM charts? No good for anybody who drives their cars in winter and actually needs a heater."
You need to go back and review chapter 1. The purpose of the thermostat is to maintain minimum operating temperature. Hopefully, your radiator has an overabundance of cooling capacity in most operating situations. So without a thermostat to regulate temperature, the engine would run too cold. Drilling a hole in the thermostat effectively creates a minimal bypass flow through the radiator. That would allow some circulation so that the thermostat could sense engine temperature. Once the engine reached minimum operating temperature, the thermostat would hold it above that floor. A 3/8" hole is my best guess as to the maximum amount of flow you could permit without totally disabling the thermostat. You’d have to experiment to get this right, and even then, it may fail you when the weather is cold
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“A solution would be to find a machine shop that could insert a brass or stainless sleeve into the thermostat housing. The inside diameter of the sleeve should be closer to the outside diameter of the sleeve on the thermostat. Then the machine shop would cut a new bypass slot in the new sleeve that better matches the travel of the sleeve on the thermostat. On the XK140 manifold, I would envision the new bypass slot being narrower and more towards the mid-point of the original factory-cut bypass slot.”
Could do that. Of course, the modern thermostat partially blocks part of the port when closed, so some of that is accomplished without any effort at all. it’s worth noting that Jaguar themselves reduced the size of the bypass slot as time went by.
I find it odd that the choke switch is located in the bypass passage of these early cars. It almost seems like the bypass was intended to leak.
In my race car, I used a blanking plate, with two 3/8ths holes in it: for THAT car, for THAT use, it worked perfectly.
Tried the same in my (then) Rover, and it ran too cold, on overrun.
Help me out Lee…on those measurements pics…and what you write…and which housing is which,.,.in the topmost pic.with tape measure…what am I looking at…with what looks like a bit more than 10/16 marks (5/8). then you say on the 140 it is .225 as seen in the lower pic with the caliper. these are two diff 140 manifolds therm locations, correct? the it says…on the 120…?
what is the slot width…once we know how far in from the face. thanks Nick
Sure…the top pic with deep-set slot is the 150 and later set-up. The slot, as measure using the stinger of my caliper, lies between .525" and .65" below the mounting surface. I must note that I did only a cursory measurement just to see if the available (aftermarket C3731/1) thermostats would function as delivered on the cars using the HD style carbs. And, the slot does have some corrosion, but I can make more precise measurements if desired. The HD carbs were used AFTER the 140, as you probably know, and Jag saw fit to design a separate water rail, incorporating the stat, to bolt onto a new (dry) intake.
XK120 has an under-abundance.
My starting carb Otter switch is located in the intake manifold, not the bypass.
Hi Lee,
Yes it would be fun to try to determine if any changes in the bypass slot dimensions could possibly be attributed to when the manifolds were manufactured.
Unfortunately I don’t know if there is a date code…here is a pic of that 140 manifolds numbers…I don’t know what they mean though…
There is also what appears to be a ‘WM6034’ cast into the other end.
Does anyone know if any of these numbers are date codes?
If we could back up a few clicks. For the 120, 140, and 150 manifolds, could I trouble someone/anyone to confirm:
-
The depth below the thermostat recess of the top of the bypass slot or tube.
-
The width of the slot or I’d of the tube.
Someone just might be trying to come up with a clever solution, so let’s be precise.
Ah HA! Looks like your manifold was cast at the “other” foundry…mine shows “West Yorkshire” and the part number (same number) is in a different spot. Different molds, different dimensions, I suppose. I could not find anything resembling a date code on mine…very few markings, indeed.
XK120 bypass ID is 1/2" as cast with a sand core, begins 1/8" below the thermostat recess and ends 5/8" below the recess.
XK140 bypass slot appears to be sand core cast, 3/8" wide, begins 1/4" below the thermostat recess and ends 5/8" below the recess.
An example of a West Yorkshire foundry logo.
The Otter switch trips off at 35 deg C so I don’t think it matters all that much whether it is in the manifold or the bypass.
[quote=“Michael_Frank, post:93, topic:377863”]
If we could back up a few clicks. For the 120, 140, and 150 manifolds, could I trouble someone/anyone to confirm:
- The depth below the thermostat recess of the top of the bypass slot or tube.
The bypass slot in the XK120 thermostat housing is circular with the top and bottom of the circular opening flattened and parallel inside of the thermostat housing. The thermostat housing is a separate casting bolted to the radiator header tank, and not part of the intake manifold. These are the measurements:
a. gasket surface to bottom of thermostat recess: .06"
b. gasket surface to top of bypass opening: .225"
c. gasket surface to bottom of bypass opening: .7"
- The width of the slot or inside diameter of the tube.
a. the roughly circular opening is .5" wide inside the thermostat housing.
Michael, on this 140 manifold with the ‘WM’ casting, upon remeasuring I still get:
- depth below thermostat recess is .30”
- width of slot is .30”
For interest sake, the diameter of the hole in the manifold where the thermostat sleeve slides up and down is 1.92”.
Thanks, folks. Those dimensions will help. I’d have to guess that the factory thermostat for these applications was different from the later units. I still think that 3171/1 would be a not too bad solution, but maybe a more accurate solution is possible. Any idea what the early saloon housings looked like? I have one here from a Mark 1, which has pretty much the same dimensions as the 3.8 E.
Note that the area of the 140’s bypass slot is at least 3 times as big as the 120’s…interesting.